Conventional wind turbines use established technology to extract energy from the wind. However, existing wind turbines are subject to a number of internal and external constraints, such as blades that are heavy, stiff, and fixed in pitch, high cut-in wind speeds, high parasitic losses, heavy and expensive components, and the need to stall blades to prevent overload. These drawbacks are particularly pronounced for development of small wind machines designed to operate at low wind speeds. At such speeds, conventional wind turbines generate very low power output and are not economically viable.
Meaningful output in light, variable winds is crucial to the economic viability of small wind machines. Providing such a viable option to communities in remote regions where there are few, if any, energy production options can expand opportunities for self-reliance and prosperity. Although electricity generation at low wind speeds may be low level output, it is still positive compared to no output at all. Thus, there is a need for a small wind energy system that can operate efficiently at low wind speeds.
Furthermore, wind gust energy is not captured in conventional wind energy systems. Most existing systems are not designed to react and quickly adjust to changes in wind direction and wind speed, i.e., wind gust changes, and therefore cannot match the direction and velocity of the wind currents. As a result, existing wind energy systems capture very little of the extra energy in wind gusts, and the gusts may cause excessive generator revolutions per minute (rpm), resulting in overloading and damage to the wind turbine. This is a significant missed opportunity. In a typical gusty wind environment, the energy in a wind gust can contain 150% more energy than the energy of the steady wind. Even small variations in wind speed can be significant for energy capture. This is because the amount of energy the wind contains is proportional to the cube of the wind speed so, for example, 12 mph wind has 73% more energy than 10 mph wind, doubling the wind speed results in eight times the power, and tripling the wind speed results in 27 times the power. Thus, there is a need for a wind energy system that can harness the energy in wind gusts.
A wind turbine blade generates its maximum lift, or power, when the blade has the correct foil shape and angle of attack for a given wind speed. However, most conventional blades are not optimized for maximum lift. As wind speed changes with gusts, turbine blade rpm changes with wind speed and the tip speed changes from root to tip. The tip speed and root speed can be very different. Maintaining constant pitch over these large speed differentials requires enormous twist. The angle of attack is correct for only one wind speed and rotor rpm, and pitch control does not maintain the correct angle of attack over the entire blade with wind speed changes. In other words, the variables of foil shape and angle of attack become ever more difficult to optimize. Thus, there is a need for an optimized blade shape to generate maximum lift during wind gusts.
Another disadvantage of existing wind turbine technology is the need for transmissions to increase rotor rpm to acceptable generator rpm. Many newer systems use large diameter generators with large numbers of field coils and/or permanent magnets. However, these systems do not allow the electricity to be connected to the 60-Hertz utility grid without the use of transformers and static inverters. Utility scale generators use speed-regulating governors to spin the generator at grid frequency. Conventional wind turbines cannot regulate the speed of the rotor, which drives the generator directly, and as a result, require the use of expensive, heavy, inefficient transformers and inverters to condition the power so it is acceptable for grid-tie. Thus, there is a need for a wind energy system that obviates the need for the transmission, transformer, and static inverter to reduce parasitic losses, reduce tower weight, and reduce related costs and costs associated with shipping and maintenance while spinning the generator at precise grid frequency.
Conventional wind energy systems cannot produce power everywhere it is needed because they are difficult to transport and install. This is because they are too large and/or heavy to transport to remote areas and require highly skilled technicians for installation. Many remote areas are not connected to a utility grid, such as indigenous communities, disaster relief areas, and military operation zones. There is a need for a portable wind energy system that can be easily transported to and installed in remote regions not connected to a power grid, and/or by consumers who want to use renewable energy, reduce and stabilize electric costs. In particular, there is a need for a portable, hydraulically self-erecting wind energy system that does not need cranes for deployment, does not require specialized skills to erect, needs minimal assembly, eliminates slab, and eliminates the need for transmission lines.
Accordingly, there is a need for a wind energy system that can operate efficiently at low wind speeds. There is also a need for a wind energy system that can effectively harness energy from wind gusts. There is a need for a wind energy system with turbine blades designed to generate maximum lift during wind gusts. There is a further need for a wind energy system that eliminates the transmission, transformer, and static inverter to reduce parasitic losses and costs associated with those components. Finally, there is a need for a portable wind energy system that can be easily transported to and installed in remote regions. In sum, there is a need for a small wind energy system that is easily transportable and installable and is economically viable at low wind speeds and in wind gusts.